It is common to come across large numbers in everyday calculations; numbers with many digits, sometimes infinitely long and that it makes no sense to consider. Let’s see how to round numbers quickly and without making mistakes.
First of all, the term “rounding digit” must be defined. If you have whole numbers, rounding will be done in the digits counting from the right of the number; that is, the digits corresponding to units, tens or hundreds. If we want to round to ten, it means that the units are not relevant, so then it will be the second digit from the right that must be rounded, that is, it will be the rounding digit. In the case of rounding to the hundredth, the third digit counting from the right of the number will be of interest. But first you have to determine which digit to round off and then identify it in the number.
The basic rule for rounding is that if the digit to the right of the rounding digit takes any of the values between 0 and 4, the rounding digit is not changed. On the other hand, if it takes any value between 5 and 9, the rounding digit is increased by one unit.
In the case of decimal numbers, the digit to be rounded must first be identified; We do this by counting to the right of the decimal point if we want to define significant figures, or to the left if the decimal number is transformed into an integer. And then the same rule applies with the next digit. In the case of the number pi of the article presentation figure, if we are only interested in three significant figures, three places to the right of the decimal point are counted and the number 1 is found. Applying the rounding rule, since the number is 5 Next, the digit to be rounded must be increased by one unit, and the rounded value of pi is 3.142. If we are only interested in the first digit, that is, to approximate it to a whole number, we must round off the number 3, which, being followed by the number 1, does not change.
Let’s look at another example. You have the number 685,374. If you wanted to round to the hundred, the rounding digit is the third to the left of the decimal point, that is, the number 6. To round, you must identify the next digit, which in this case is 8. Since 8 is between 5 and 9, one unit must be added to round off, and the number rounded to the hundred is 700. In case of rounding to the unit of one thousand, that is, four digits to the left of the decimal point, it is observed that we do not have any number, so we add a digit 0. Since 6 is between 5 and 9, we must add a unit to the rounding digit, and the rounded number is 1000. If we were only interested in the number with a significant figure, that is, with a single figure after the decimal point, we identify the rounding digit by counting one position to the right of the decimal point; the 3. Applying the rounding rule, the number in question rounded to one significant figure is 685.4.
In a daily application, to quickly calculate the tip that we would like to leave when paying the bill in a bar, it can be estimated at 10% of the value of our consumption. You can quickly round the consumption and divide it by 10. If you are paying for a consumption of $37.55, rounding the last digit gives a value of $40, and therefore the tip will be $4.
Fountain
Arias Cabezas, Jose Maria, Maza Saez, Ildefonso. Arithmetic and Algebra . In Carmona Rodríguez, Manuel, Díaz Fernández, Francisco Javier, eds. Mathematics 1. Bruño Editorial Group, Limited Company, Madrid, 2008.
